Alternatively you could create the following "Java Application" launch configuration and launch it directly from Eclipse:

Main class

org.codehaus.classworlds.Launcher

classpath

%M2_HOME%\boot\classworlds-1.1.jar

VM arguments

-Dclassworlds.conf=%M2_HOME%\bin\m2.conf
-Dmaven.home=%M2_HOME%

Program arguments

<maven cli arguments>

Debug Maven using m2eclipse

With m2eclipse you can debug Maven core and Maven plugins while running goals using m2eclipse's "Maven Build" external tools launch configuration (or from Run As / Maven * shortcut from the popup menus). Simply put a break point in the corresponding classes and switch to the Debugger perspective.

You can also configure Maven surefire plugin to not fork new JVM to run tests and then you can even debug test classes launched using "Run As / Maven test" shortcut: